Yeah I wish I could do that but I don't have the money to buy a double set of drives. I often upgrade my NAS by just swapping out a disk for a bigger one and the old one goes into the backup rotation. Right now I have 15 disks in there (and 8 in the actual NAS). Because they are of course smaller drives I need more of them to cover the content.

Buying hardware to keep 15 disks spinning is also pretty expensive :(